Thermally conditioned machine tool



B.- SASSEN 2,070,81-1

THERMALLY CONDITIONED MACHINE TOOL Feb. 16, 1937.

Filed July 28, 1934 2 Sheets-Sheet 1 Va ow I 4' Feb. 16, 1937. B SASSEN 2,070,811

THERMALLY CONDITIONED MACHINETOOL Filed July 28, 1934 2 Sheets-Sheet 2 Patented Feb. 16, 1937 PATENT OFFICE THERMALLY CONDITIONED MACHINE TOOL I Bernard Sassen, Cincinnati, Ohio, assignor to The Cincinnati Milling Machine Company, Cincinnati, Ohio, a corporation of Ohio Application July 28, 1934, Seral No. 737,468

8 Claims.

This invention relates to metal working machines, and more particularly to improvements in an hydraulically operated-machine tool.

One of the objects of this invention is to improve the accuracy of hydraulically operated machine tools by controlling the thermal condition thereof. 7

Another object of this invention is to provide a machine tool which will have a substantially constant temperature under all operating conditions, thereby preventing inaccuracies caused by uneven expansion and contraction of various parts which were previously'due' to heating up of the machine.

Another object of this invention is to provide a fluid operated machine tool in which the fluid is of substantially constant viscosity throughout any given period of operation of the machine.

A still further object of this invention is to eliminate all compensating devices on hydraulically operated machine tools, and provide a single automatic control means for maintaining the machine and operating parts at a constant temperature.

An additional object of this invention is to provide a fluid operable delayed trip controlled mechanism in which the timing of the delay will always be the same for any given adjustmentthereof. ,p

A still further object of this invention is to provide a remote control fluid operable mechanism for determining the position of a part which will insure that the position of the part will always be the same for any given setting of the control.

Other objects and advantages of the present invention should be readily apparent by reference to the following specification, considered in conjunction with the accompanying drawings illustrative of one embodiment thereof, but it will be understood that any modifications may be made in the specific structuraldetails thereof within the scope of the appended claims without departing from or exceeding the spirit of the invention.

Referring to the drawings in which like reference numerals indicate like or similar parts:

Figure 1 is an elevation of a machine tool embodying the principles of this invention.

Figure 2 is a detailed section on the line 2-2 of Figure 1.

Figure 3 is a section on the line 33 of Figure 1.

Figure 4 is a detailed plan View of the trip control mechanism.

Figure 5 is a semi-diagrammatic view of the fluid control circuit of the machine.

In the quest for greater accuracy in machine tools, the detrimental effects of heat have been known but prior attempts to offset these effects 5 have been confined to compensating devices applied locally at presumed strategic points, but no attempt has been made to prevent temperature changes in the first instance, thereby eliminating the trouble at its source. This invention is di- 10 rected to improving the accuracy of machine tools by thermally conditioning the same, and a milling machine such as shown in Figure 1 has been selected to exemplify this invention.

' In this type of machine tool, as in many other 15 types, stock removal is accomplished by effecting relative movement between a tool and work piece. This is accomplished in the machine shown by applying the work piece to the table I0 which is reciprocably mounted in guideways 20 formed on the top of the bed II and moving the table past the tool I 2 which is rotatably supported by the column l3 and power driven through suitable conventional means not shown, from a power shaft M which, as shown in Fig- 5 ure 5, is actuated by a prime mover l5.

As shown in Figure 5, the table may be moved by a fluid operable motor-in the form of a cylinder l6 having a contained piston I! which is operatively connected by a piston rod l8 to oppo- 30 site ends of the table II]. A pair of channels l9 and 20 are connected respectively to opposite ends of the cylinder and it will be apparent that when pressure fluid is delivered by. one of these channels to the cylinder and the other channel 35 connected to exhaust, that the table will be moved. In prior devices of this nature, the fluid delivered to the cylinder gradually becomes heated when the machine is operating under a heavy production schedule due to the wire-drawing effect of throttles and relief valves and the forcing of large quantities of fluid at high velocities through the piping. As the temperature of the oil rises, the piston rod l8 necessarily becomes 45 heated, with the result that the same expands and due to unequal expansion thereof relative to the table ID, a tendency is created for the table. to buckle slightly which means that work surfaces displaced from the center of the table will 50 have more material removed therefrom than work surfaces located in approximately the center-of the table. By means of the presentinvention, the fluid delivered to the cylinder [6 is maintained at a substantially constant temperanected. This valve also has ports 26 and 25 which are connected by channels 26 and 21 to I ports 28 and 29 respectively of a reversing valve cent the edge of the work table.

36. The reversing valve alternately admits pressure fluid to channels 26 and 27 to cause reciprocation of the table. The plunger 3| of the stop valve has a cannelure 32 which is flanked by spools 33 and 36 so that upon movement of the plunger 3| to the left as viewed in Figure by the operatively connected controllever 35, the ports 26 and 25 are interconnected by the cannelure and the spools 33 and 66 close ports 22 and 23. This prevents escape of fluid from the cylinder l6 but permits the incoming flow through either channel 26 or 21 to be by-passed to reservoir, thereby preventing undue load on the pump and the creation of excessive high pressures in the system.

The reversing valve 30 has a pressure port 36 and a pairof return ports 31 and 38. This valve has a plunger 39 in which is formed a first cannelure 60 for alternately connecting port 29 to the pressure port 36 or exhaust port 38; a second cannelure 6| for interconnecting port 28 to return port 31 when the plunger is to the left; and with pressure port 36 when the plunger is toward the right.

- The position of the reversing valve plunger is controlled by a pilot circuit including a pilot valve 43 having a port 66 connected by channel 45 to the right hand end of the reversing valve housing, and a second port 66 for supplying fluid to the left end of the reversing valve. The pilot valve has a pressure port 4'! which is alternately connected by the cannelure 48 in the valve plunger with ports 44 and 46 to effect shifting of the reversing valve plunger by power. The valve plunger 49 also has a cannelure 56 for connecting port 46 with a return port 5| when the plunger is toward the right, and a second cannelure 52 for connecting port 64 with a return port 53 when the plunger is shifted to the left.

The plunger 49 is extended and operatively connected through suitable means such as a ballended lever 54 with a trip controlled shifter rod 55. This rod extends upward to a position adia- As shown in Figure 2 the ball-ended lever 54 has a lost motion connection with the valve plunger 69 and also has a pair of indents 56 and 51 which-are alternately engaged by the spring pressed detent 58. This constitutes a load and fire mechanism which insures complete shifting of the pilot valve.

The rod 55 has a lug 59 projecting radially from the side thereof opposite to the table, which is alternately engageable by dogs 66 and 6| for automatically changing the direction of movement of the table. The rod also has integrally secured thereto the manually-operable handle 62 whereby the direction of movement of the table may be changed at will by the operator.

In machine tools of the nature disclosed, it is often desirable that aslight delay occur between the time of tripping the reversing mechanism and the actual start of the table in its new direction. This delay is to permit the tool to clean up before retracting from the work. One form of delay mechanism is shown herein and comprises a valve 63 having a port 64 in one end thereof which is connected by channel 65 to the port 46 of thepilot valve. When pressure is admitted to channel 65 to shift the reversing valve plunger to the left, the fluid entering port 66 acts on the end of valve plunger 66 to shift the same axially, but the fluid in the opposite end of valve 63 is prevented from escaping at a fast rate by a throttle valve 61 which is interposed between a port 68 of valve 63 and port 46 of the pilot valve. The throttle valve 61 has an adjustable plunger 69 which determines the rate of escape of fluid from the upper end of valve 63 and thereby the timing of the delay. This is true because port 66 cannot be connected to port 16 and thereby through channel TI to port 72 of the reversing valve until the plunger 66 has moved upward a sufficient amount for the spool 13 thereof to uncover port 19. In prior devices of this nature utilizing a throttle valve, the viscosity of the fluid plays an important part because if the fluid was very cold and thick, the time of delay for a given setting of the throttle valve was considerably longer than when the fluid was hot and limpid. This meantthat the tool in some cases had more than enough time to clean up the cut and in other cases not enough time. It will thus be seen that the results vary even although the throttle valve had the same setting. By means ofthe present invention the temperature of the fluid is maintained sufliciently constant that the viscosity of the fluid does not vary sufliciently to produce any marked change in the time of delay for a given setting of the throttle valve.

When the pilot valve is tripped to the position shown in Figure 5, the plunger 66 is in an extreme upward position, and the pressure from port 44 flows through channel 65 to immediately shift plunger 39 and at the same time it flows through channel I4 to the throttle valve, but since the valve is closed to such an amount as to prevent a rapid flow to valve 63, a by-pass check valve is provided in parallel with the throttle valve so that the fluid will be immediately by-passed around the throttle valve and immediately efiect downward shifting of plunger 65. Upon completion of this downward movement, the plunger 66 will interconnect port ID with return port 16 thereby permitting free exhaust of fluid from port I2 and an immediate shifting of the reversing valve.

Pressure fluid is supplied to the system by a pump 'I'I which is driven from the shaft H which in turn is actuated by the prime mover l5. The pump has an intake 18 for withdrawing fluid from a reservoir and delivering the same under pressure to channel 19 which channel is connected to port 86 of a rate control valve 8|. A channel 19 has a branch 82 which supplies fluid pressure to port 41 of the pilot valve. It also has a second branch 63 which is connected to port 84 of a differential valve 85. The rate control valve 8| has a port 66 which is connected by channel 81 for delivering fluid to pressure port 36 of the reversing valve. Channel 81 has a. branch 88 connected to port 89 of the differential valve 85. From the foregoing, it will be seen that the pressure in channel 19 acts on the left end of plunger 66 which is reciprocably mounted in valve 85 and the opposite end of the plunger is acted upon by the pressure in channel 81. Except when the throttle valve BI is wide open and even then to a slight extent, there is a pressure drop the opposite end. A spring 9| is inserted in the valve 85 and the pressure of the spring plus the pressure in channel 88 is always equal to the pressure in channel 19 and should the pressure become unbalanced so that the pressure in channel 19 is greater, the plunger 90 will move toward the right and uncover port 92 permitting escape of a certain amount of fluid to equalize the pressures. The differential valve 85 thus acts to maintain a constant pressure differential across the throttle valve regardless of the load conditions on the table and regardless of the rate of table movement. The throttle valve has a plunger 93 which is movable with respect to port to open and close the same and thereby determine the feed rate of the machine, which feed rate will be constant for a given setting of the plunger 93 because the difierential valve automatically takes care of the load conditions.

The valve M has a port 94 which is connected by a branch line 95 to the return line 96 from the reversing valve. Channel 96 is connected to port 91 of the feed rate control valve 98. This valve has a plunger 99 mounted therein for controlling the rate of escape of fluid from channel 96 to the return port I00 and thereby determining the pressure in channel 96 which in turn determines the pressure on the left end of plunger .93 of throttle valve 8|. A second plunger IUI is reciprocably mounted in valve 98 and a spring I92 is interposed between plunger I0! and plunger 99. The plunger IllI is held in contact by the spring I02 with the periphery of a rotatable cam I033. The cam is keyed to the end of shaft I04 which shaft, as shown in Figure 3, projects through the front wall of the machine for receiving a bifurcated collar I05. A manually operable control lever I06 is pivotally mounted between the bifurcations of the collar. One end of the lever has a v-shaped end It! adapted to selectively engage similarly formed teeth I 98formed on the face of a supporting plate I 09. A spring pressed ball IIIl serves to normally maintain the V-shaped end of the lever'in engagement with the teeth and thereby hold the cam I03 in its various adjusted positions. By depressing the knob .III, the operator can rotate the cam and thereby variously position the plunger 99 relative to the port I to determine the pressure acting on the left end of plunger 93. A spring H2 continuously acts on the right end of plunger 93 and thereby against the fluid pressure acting to shift the plunger. Since the plunger 99 acts as a throttle valve, the pressure in channel 96 will depend for a given position of plunger 99 upon the viscosity of the fluid, but in the present instance means have been provided for maintaining the temperature of the fluid substantially constant whereby its viscosity will be substantially constant and the feed rate indicated by the pointer H3 moving over the scale H4 will be the true feed rate.

The means for thermally conditioning the machine will now be explained. The main reservoir II5 is formed by the structural walls of the bed II so that the fluid therein is in direct contact with the walls. This means that if the temperature of the fluid is maintained substantially constant, the temperature of the walls will also be maintained substantially constant, thereby preventing expansion or contraction thereof.

The machine is also provided with an auxiliary reservoir H8 which is formed in the upper part of the column I3 by casting a horizontal wall II! in the column integral with the side walls thereof. The fluid in this reservoir is also in direct contact with the side walls of the column as well as the wall II! which in reality forms the floor of the auxiliary reservoir. shown in Figure 5, this auxiliary reservoir may be interposed in the return lines so that the returning fluid will collect in this reservoir to a predetermined height as determined by the height of the over-flow pipe II8 above the floor Hi. This pipe returns the overflow to the main reservoir. If the fluid in reservoir II B is now maintained substantially constant and nearly equal to the temperature of the fluid in reservoir II5, it will be seen that the walls of the column will be substantially the same temperature as the walls of the bed and no unequal expansions between the two will occur to throw the tool out of alignment with the work.

The temperature and thereby the viscosity of the operating fluid in these reservoirs is maintained substantially constant by cooling coils I I9 and H9 which are serially connected to any well-known form of compressor unit I20 which circulates a cooling medium through the coils. The compressor may be actuatedby an electric motor I2I, the motor having a pair of leads I22 and I23 connected to any conventional form of thermostatically controlled switch mounted in the switch box I24. The switch in box I24 is controlled by a thermostat I25 which is located in the reservoir II5 so that the compressor will be automatically actuated by the motor I2I whenever the temperature of the fluid varies from a predetermined standard to which the thermostat is adjusted.

The prime mover I5 and the switch box I24 may be connected in parallel to switch points I26 and I2! for joint control by the main switch I28. Thus the operation of the whole machine may be controlled from a single main switch.

It will now be seen that with the operating fluid and the air in the chambers closely associated therewith maintained at a constant tern?- perature, and these in turn assisting to maintain the temperature of the structural walls of the machine constant by contact therewith, that the relative relation between the tool and work will be constant throughout any period of operation of the machine; and since the viscosity of the fluid will be constant because its temperature is constant, the feed rate of the machine will be the same throughout any period of operation.

There has therefore been provided an hydraulically operated machine tool that has improved accuracy in the sense of maintaining the relative position between tool and work during any period of machine operation; that has means for maintaining any selected feed rate regardless of work done and that has accurate respondence at all times between controls and the parts controlled.

What ls claimed is:

1. In a fluid operable metal working machine having a tool spindle and a work support, the combination of fluid operable means for effecting relative movement between the supports, a fluid reservoir, pumping means for delivering fluid from the reservoir under pressure to said fluid operable means, power operable mechanism for maintaining the temperature of the fluid in said reservoir substantially constant, additional power operable means for driving said spindle and 4 aoraeii pumping means, and a common control for both of said power operable means.

2. In a fluid operable metal working machine having a tool spindle and a work support, the combination of fluid operable means for efiecting relative movement between the supports, a fluid reservoir, pumping means for delivering fluid from the reservoir under pressure to said fluid operable means, power operable mechanism for maintaining the temperature of the fluid in said reservoir constant, additional power operable means for driving said spindle and pumping means, a common control for both of said power operable means, and an auxiliary control for determining operation of one of said power operable means independently of the other.

3. In a machine tool structure having a chamber formed in part by structural walls which support one of the movable elements of the machine, the combination of a fluid reservoir formed in said chamber with the fluid in direct contact with said walls, means to utilize the fluid in said reservoir for actuation of a movable element of the machine, and means to maintain the walls of said chamber and the fluid in said reservoir at a substantially even temperature to prevent expansion of the walls and to maintain the rate of operation of the movable element constant, including a cooling coil mounted in said reservoir and power operable means for circulating a cooling medium through said coil.

4. In a machine tool having a fluid operable part, the combination of a reservoir containing a body of operating fluid, means for supplying said operating fluid to said part, means for cooling said fluid, and means in the body of the fluid and responsive to rises in the temperature thereof to eiTect operation of said cooling means and thereby inverse changes in the temperature of the fluid whereby the viscosity of the fluid may remain substantially constant.

5. In a machine tool having a work support and a tool support, the combination with a fluid operable motor for efiecting a relative feeding movement between the supports, of a reversing mechanism for changing the direction of said relative movement including a fluid shiftable device, means to supply an operating fluid for shifting said device, means to delay the flow of said operating fluid to said device including a throttle valve positionable to determine time of said delay, and means to maintain the viscosity of the fluid passing through said throttle valve substantially constant whereby the time of delay will always be the same for a given setting of the valve.

6. A thermally conditioned machine tool comprising structural walls for supporting and guiding a work table for relative movement with respect to a metal removing tool, an hydraulic circuit for actuating said table including an hydraulic motor, throttle means for controlling the rate of fluid delivered to and from said motor and thereby its rate of operation, a fluid reservoir formed by said walls, means for pumping fluid from said reservoir into said circuit and means in the reservoir for maintaining the fluid contained therein at a substantially constant temperature, whereby a given setting of said throttling means will produce -a substantially constant rate of table movement.

7. A thermally conditioned machine tool comprising structural walls for supporting and guiding a work support and a metal removing tool for relative movement, means for effecting said movement including an hydraulic operating circuit consisting of a fluid operable motor operatively connected for effecting said movement, a throttling device for governing the rate of fluid consumption of said motor, and means for supplying said throttling device with fluid at constant temperature including a reservoir formed in part of said walls, a thermostatically controlled cooling system for maintaining the body of fluid in said reservoir at a constant temperature, a power operable means for withdrawing fluid from said reservoir and delivering the same to said throttling device whereby for a given setting of said device the resultant rate of said relative movement will remain substantially constant.

8. In a machine tool having a work support and a tool support, the combination with a fluid operable circuit for efiecting relative movement between said supports including a reversing valve, of a pilot control circuit for shifting said valve including a fluid operable delayed trip mechanism, and means for supplying fluid at a. constant temperature to said delayed trip mechanism whereby the delay efiected thereby will be substantially constant including a reservoir of fluid, thermostatically controlled means for maintaining the temperature of said fluid constant, and power operable means for delivering said fluid to said delay trip mechanism.

BERNARD SASSEN. 

